In the case where one outdoor unit controls plurality of indoor units, it is necessary that addresses be set at the indoor units in order to transmit a control signal. The same holds true for the case in which one remote controller transmits the control signal to the plurality of indoor units.
In the conventional air conditioner, the outdoor unit or the remote controller requests a unique serial number of each indoor unit in each digit, the indoor unit responds to a number of the requesting digit, to detect the serial number, and the address setting is performed to the indoor unit having the serial number.
During the address setting, when the address setting is not normally performed because the indoor unit cannot normally receive a command for requesting a predetermined digit of the serial number due to a noise or ringing or the like, the address setting starts over by returning to the initial digit to detect the serial number again. For example, Patent Documents 1 to 3 disclose a technique concerning the address setting of the air conditioner.
Patent Document 4 also discloses a technique of preventing reception failure caused by the noise. In the technique disclosed in Patent Document 4, a whole time and a low time of a pulse signal are detected, and the whole time and the low time are compared to reference times to detect a start bit signal.    Patent Document 1: Japanese Patent Application Laid-Open No. 9-196443    Patent Document 2: Japanese Patent Application Laid-Open No. 9-257295    Patent Document 3: Japanese Patent Application Laid-Open No. 2000-74461    Patent Document 4: Japanese Patent Application Laid-Open No. 6-181592